Improve file change notify with inotify and "vfs mkdir use tmp name"

Same code survived a pipeline as https://gitlab.com/samba-team/devel/samba/-/pipelines/1840912648, this just carries Bug: tags.

I'm still struggling to get this through "make test" when adding smb2.notify to the normal runs on "fileserver". Running smb2.notify now completes successfully with "kernel change notify = yes" with and without O_PATH. Notify with inotify was not tested before this MR, so it's not a test regression.